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Date:      Fri, 1 Sep 2000 12:25:36 +0930
From:      Greg Lehey <grog@lemis.com>
To:        John Turner <john@drexeltech.com>, freebsd-questions@FreeBSD.ORG
Subject:   Re: Tagged Queueing question
Message-ID:  <20000901122536.B5586@wantadilla.lemis.com>
In-Reply-To: <20000831131350.F2264@absinthe.condo.chico.ca.us>; from fred@condo.chico.ca.us on Thu, Aug 31, 2000 at 01:13:50PM -0700
References:  <4.3.2.7.0.20000830083308.00b197f8@mail.johnturner.com> <20000831104349.E29115@wantadilla.lemis.com> <20000831131350.F2264@absinthe.condo.chico.ca.us>

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On Thursday, 31 August 2000 at 13:13:50 -0700, Fred Condo wrote:
> On Thu, Aug 31, 2000 at 10:43:49AM +0930, Greg Lehey wrote:
>> On Wednesday, 30 August 2000 at  8:35:41 -0400, John Turner wrote:
>>>
>>> This message showed up in one my server's security check output
>>> today.  I've never seen it before.  Is it something I need to worry
>>> about?  The server was rebooted yesterday, after about 2 months of uptime.
>>>
>>>> da1 at ahc0 bus 0 target 2 lun 0
>>>> da1: <IBM DNES-309170W SAH0> Fixed Direct Access SCSI-3 device
>>>> da1: 80.000MB/s transfers (40.000MHz, offset 30, 16bit), Tagged Queueing Enabled
>>>> da1: 8748MB (17916240 512 byte sectors: 255H 63S/T 1115C)
>>
>> Tagged queueing is a technique where the driver issues multiple
>> requests to the controller, and the controller automatically continues
>> with the next request after finishing the first, without needing
>> intervention by the driver.  This improves performance.  There's
>> nothing to worry about.
>
> Unless you have certain seagate drives. There was a discussion of
> seagate firmware bugs recently on -questions or -stable. That bug bit
> me until I disabled write-through on the scsi bios and used camcontrol
> to turn off tagged queueing at boot time. The original questioner's
> IBM drive should be okay AFAIK.

This is a separate issue.  Yes, some drives have broken tagged
queueing.

Greg
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